The invention relates to a welding torch as generically defined by the preamble to claim 1 and to a stream nozzle as generically defined by the preamble to claim 8.
The stream nozzle, also known as a contact nozzle, typically comprises electrolyte copper, or a more-wear-resistant copper-chromium-zirconium alloy. Other variant alloys also exist, for instance with beryllium. The task of the stream nozzle is to transmit current to the electrode wire and to guide it. For good process safety, an optimal current transfer from the nozzle stock to the stream nozzle is necessary. Moreover, the stream nozzle must transmit considerable heat over the mounting region. In practice, until now, stream nozzles have predominantly been used without surface treatment, that is, bare or bare to the copper; they are secured replaceably to the nozzle stock via a screw connection or a plug-type connection. In welding, welding beads or welding splashes that occur exhibit the undesired tendency to adhere to the exposed surface of the stream nozzle. This can cause adverse effects on the flow conditions for the inert gas that glows on the outside along the stream nozzle to the welding point. Welding splashes adhering to the end face and in the vicinity of the exit from the electrode wire duct can hinder advancement from friction with the electrode wire. In practice, stream nozzles are therefore known that at least on their jacket face and end face have a metal coating, in the form of chromium- or nickel-plating. This coating is intended to provide improved reflection of the arc radiation (reduced heat consumption) and also to prevent the welding splashes from adhering (anti-adhesive effect). Not only are coatings formed by chromium- or nickel-plating expensive; they do not meet the expectations made of them to a satisfactory extent.
In addition, whenever the coating extends into the mounting region of the stream nozzle, current transfer problems occur; this is suspected to be because the current transfer fluctuates as a function of the layer thickness. In applying the coating, it is therefore necessary that the application region intended for the current transfer be covered as well. This is expensive.
The object of the invention is to disclose a welding torch of the type defined at the outset, and a stream nozzle for this kind of inert gas welding torch, that makes it economically possible to achieve an optimal anti-adhesive and reflective action. A part of the object is also that the metal coating have no adverse influence on the current transfer but instead even improve the current transfer.
The stated object is attained by the characteristics of claim 1 and claim 8, respectively.
Surprisingly, a silver coating leads to excellent anti-adhesion and reflective effects. Even if the silver coating is meant to extend into the mounting region, it has no adverse effect on the current transfer but in fact even improves the current transfer. The heat transfer capability of a silver coating is already optimal. Applying the silver coating can be done economically, particularly in mass production. Since the silver coating has no adverse effect on the current transfer and in fact even improves it, when the coating is applied there is no need to cover regions of the surface that are important for the current transfer. This makes coating the stream nozzle simpler.
Expediently, the coating comprises galvanically or chemically applied contact silver. Contact silver can be applied with the desired layer thickness and good adhesion to the material comprising the contact nozzle at low equipment expense.
The coating should have an essentially uniform layer thickness, preferably between about 6 and 10 xcexcm.
The silver coating should be uniform, at least on the jacket face and the free end face of the stream nozzle.
However, it is especially expedient for the entire surfaces of the stream nozzles to be provided with the silver coating. This simplifies the procedure in galvanic or chemical coating of the stream nozzle considerably. The silver coating, which is also present in the region of attachment to or contact with the nozzle stock or inner tube of the torch as well, leads to optimal current transfer and heat transfer and makes an important contribution to process safety.
In a stream nozzle with a screw attachment for producing a screw connection to the nozzle stock or the inner tube of the torch, the male thread of the screw attachment is also covered with the silver coating.
A stream nozzle with a plug-in attachment for producing a plug-type connection to the nozzle stock or inner tube of the torch is also covered with the silver coating on the fitting faces of the plug-in attachment.
Other metal spraying methods are naturally also practicable for applying the silver coating.